In order for wireless networks operators to solve one of their biggest problems—how to achieve higher signal strength where one needs or wants it most, they have started to deploy their own or rely on end users to buy personal devices that act similarly to the Wi-Fi routers, in order to provide nearby cellular bandwidth in hard-to-reach places like offices and homes.
Therefore, the newest type of cell sites, named femtocells (a femtocell—originally known as an Access Point Base Station—is a small cellular base station, typically designed for use in a home or small business) are setting out to solve carriers' often-expensive problem of providing complete coverage. Mobile terminals such as mobile phones usually work well in metropolitan areas, but when traveling a few miles off these areas e.g. into the countryside, the signal strength drops rapidly. Also, most frustrating to many people is that the signal strength at their homes or inside offices is often unusable.
Thus, according to the femto solution the end-users may buy small femto devices that are personal cellular sites. The femto device has an antenna to boost the available signal as well as an Internet connection. The device uses the end user Internet connection to connect to the service provider's network and to route the user's phone calls. Normally, femtocells operate within the operator's licensed spectrum.
Typically, the cells of the wireless network may be divided into the following three categories:
First category—Protected cells, for example macro-cells that may extend for example for about 1.5 km from the base station in sub-urban deployment at frequencies being around 2.5 GHz;
Second category—Regular cells, for example micro-cells that may extend for example for about 300 m from the base station in urban deployments or relay cells; and
Third category—Cells such as femtocells, which include a base station and subscriber terminal(s) that might create meaningful interference to MSs of the other cells. The typical operation range of a femtocell is 30 m.
As will be appreciated by those skilled in the art, scenarios that entail an overlapping deployment while using the same or adjacent frequency channels between two (or more) cells of these categories, are generally possible. However, with the exception of femtocells, which may not belong to the mobile operator, the BS-MS interference can simply be resolved by applying a hand-over process following which the MS will be serviced by the BS that is responsible for the creation of interference thereto. In the case of femtocells, the hand-over is limited to such situations where the user's access is allowed by the target cell. A femto Base Station, which is typically owned by a private home user, may provide service only to the mobile terminals belonging to that user.
The problem yet to be solved is the reduction in interference due to overlapping that may exist between a femtocell and any of the other cells. The most problematic interference problem would be noticeable when a MS belonging to a macro-cell operates at the proximity of a femto-BS.